The present invention relates to a differential mass flowmeter.
The use is known of flowmeters comprising a substantially U-shaped tube with the ends inserted in a rigid support, which is caused to oscillate, by exploiting the elasticity of the material, about an axis passing through the portions inserted into the support.
During such oscillation, if the tube is empty, the arrangement of the portion thereof opposite the support remains unchanged, while if the tube is conveying a flow of fluid, the known Coriolis forces give rise to an inclination of said portion in one direction during the downward motion and in the opposite direction during the upward motion.
The angle of said inclination is proportional to the mass flow rate conveyed by the tube, and it is then sufficient to provide said tube with means which allow the measurement of said angle to obtain, by means of suitable signal processing, a continuous indication of said flow rate.
This kind of flowmeter is very widespread, among other applications, for the measurement of the variations which occur in the flow rate of a fluid during the passage through an apparatus; this measurement, which is performed, e.g., on the dialysis liquid entering and leaving a haemodialysis filter in order to evaluate the amount of the ultrafiltrate, i.e. the amount of water with electrolytes which passes to said liquid from the blood of a patient during its passage through the filter, is achieved by arranging one filter downstream and another one upstream of the device, but this method has many disadvantageous characteristics, such as high cost and the possibility of disturbances in the measurement.